UV radiation is an invisible electromagnetic radiation in the wave length range from 100 nm to 400 nm. This range is being divided into the sub-ranges UV-A, UV-B and UV-C.

UV radiation is being applied in various areas of industry, science and medicine such as food industry, textile industry, mineralogy, forensics. In addition to that UV radiation is being applied in the field of spectroscopy, X-ray microscopy, nanoscopy, photo lithography, as well as for disinfecting and for polymerisation of synthetic materials, lacquers, glues etc.

Needless to say that UV sources are used in NDT for excitation of inspection media fluorescence. Testing is to be carried out by the means of UV-A radiation (315 to 400 nm) with nominal maximum radiation intensity at 365 nm. On the surface to be inspected the irradiation intensity must be larger than 1000 μW/cm² at ambient illumination of less than 20 Lx.

Nowadays along with state-of-the-art UV LED lamps the conventional low-pressure, medium-pressure and high-pressure metal-halide lamps are also used in all kinds of industrial applications. Normally those are mercury gas discharge lamps with/without additional doping elements such as gallium, indium, iron and led.